Bug report: N-queens is not using multiple cpu cores
Please see the Phoronix Test Suite results HERE for a guide showing how I found this bug.
I am in the process of running updated tests that enable both cores on my Core 2 Duo but keep the 800 Mhz speed limit for use in making benchmarks related to the recent Phoronix article on Cortex A9s vs. a single-core Atom at 1Ghz (http://www.phoronix.com/scan.php?pag..._arm_x32&num=1). My first run was using my 4-year old notebook with a single core disabled on the CPU and the other core limited to 800 MHz. Next, I re-ran the benchmarks with both cores activated, but both cores also being limited to 800 Mhz. Of course, I have had some big speedups in multi-threaded applications... with the notable exception of n-queens!
I have made multiple runs of the n-queens benchmarks, and as you can see from the results page, there is basically zero speedup between the "Core_2_Crippled" system with only one core turned on vs. the dual-core setup. Look at the other benchmarks that do use multi-threading and you'll definitely see that multi-threading is working on this machine, just not on the N-queens benchmark.
Please note: I have confirmed that the binary being executed is the 'qn24b_openmp' binary that is supposed to be multi-threaded through OpenMP. I have run the binary manually and through the standard PTS runs, and it does not use my second CPU core whatsoever. I think there is a bug in PTS that should get fixed. I'm running version 4.0.1 BTW.
No news on the bug, but the first link in my post wasn't going to the right place. Please go here: http://openbenchmarking.org/result/1...SU-1209058SU45 for the test results.
pts/n-queens-1.1.0 - http://openbenchmarking.org/test/pts/n-queens - ensures the OpenMP flag is passed to the compiler. Thanks.
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